Several printing techniques are widely used in the printing industry, among which is a printing technique known in the printing field as “Gravure press” and “rotogravure printing”.
Typically, the manufacturing of a gravure printing cylinder involves coating a cylindrical metal base (for example steel) with an “image carrier” (for example copper); polishing the surface of the image carrier; engraving (such as by etching) the image on the image carrier; coating the image carrier with wear-proof layer (for example Chrome plating) to increase the print durability of the printing cylinder; and polishing the wear-proof layer.
During printing, the printing cylinder is immersed in a bath of fluid ink and as it rotates in the bath, ink fills the tiny cells and covers the surface of the cylinder. At a certain point, while the cylinder keeps on turning, the excess ink is wiped off the cylinder by a flexible steel doctor blade which leaves the non-image area clean while the ink remains in the recessed cells. The ink remaining in the recessed cells forms the image by direct transfer to the substrate (paper or other material) as it passes between the plate cylinder and the impression cylinder. The ink is drawn out of the cells onto the substrate by capillary action at the point of contact. In many cases, gravure printing is done using engraved copper cylinders protected from wear by the application of a thin electroplate of chromium. Gravure printing generally consists of a printing cylinder, a rubber covered impression roll, an ink fountain, a doctor blade, and a means of drying the ink. The major unit operations in a gravure printing operation are (i) Image preparation; (ii) Cylinder preparation; (iii) Printing, and (iv) Finishing.
Gravure press offers an outstanding print quality, output consistency, high versatility and printing speed. Gravure press also allows producing excellent and constant reproductions throughout each print run. Gravure press is a relatively simple printing process that can produce millions of high quality copies at high speed. Nevertheless, defects may occur at any fabrication step of the printing cylinder, and thus, it would be advantageous to visually inspect the printing cylinder throughout its fabrication process. In order to significantly reduce costs involved in the fabrication of defective printing cylinders, the printing cylinders require a careful scrutiny throughout various steps of their fabrication process. In cases where defects are minor or located in non-critical positions (depending on the patterning scheme), the printing cylinder may be used after removing, or fixing, the defects, or with the defects. In cases of major or critically located defects, it may be decided that the printing cylinder will not be used.